newbie trying to set up network

[Nullman]

in all honesty - is there anyone around who has used something like this method before that would be willing to walk me through it?

Not only i use it every day for the last 12 years, i implemented such solutions to a lot of people. And they use it for many years not even thinking about it.

is it complicated for a networking newbie?

Its not complicated. Once you figure out how to configure interfaces in opnsense, you are pretty much set. How are you going to configure your access point depends on what that device actually is.

I have already set up opensense box on a mini pc (and gone through some of the settings / watched many tutorials / learned a lot about networks)

In this case, the most complicated part for a newbie would be configuring additional port on opnsense to work on a different subnet. Once you do that, you just attach access point to that port, and you are done.

I have just never worked through using a wireless access point (I feel so old fashioned, lol)

Its because there are endless ways on how you can do this. Not all of them are correct though. Especially if security and performance are your priority. Just because some solution works doesnt mean its implemented correctly.

Much of it is new to me also but in my unqualified opinion an opnsense router coupled with openwrt access point(s) is an appealing combo for a home user. You are able to re-purpose your existing gear or buy cost effective secondhand and there is ample documentation on both. I have a couple of meraki units, running openwrt in 'dumb AP mode', connected via a small managed switch.

Repurposing your old gear is nice if your gear comes from reputable manufacturer that does things correctly,. OpenWRT is great. I love it. However, running OpenWRT on TP-Link is not the same as running it on Cisco Meraki. TP-Link has critical flaws in its hardware and how it handles its port during device booting. Cisco Meraki has no such issues. And lets not even go into build quality and internal hardware choices.

You can in theory connect the APs directly to the opnsense box, but this can lead to interface issues on the router side. Check out the openwrt guides for access point only mode. Then consult the docs here for opnsense vlans.

You just need to make sure that your wireless device is working in AP mode. Avoid running wireless devices in router mode because then you have NAT and additional DHCP server which are not needed in this case.